A piston reciprocates within a cylinder of an internal combustion engine and compresses fluids, such as gases, within a combustion chamber of the cylinder. These compressed fluids are then ignited to expand within the combustion chamber thereby forcing the piston away from the point of ignition and cycling the piston to its original position.
Piston ring assemblies are typically received within an annular groove disposed about an outer periphery of a piston. The primary function of piston ring assemblies is to provide an effective seal. This is typically accomplished by placing a first piston ring assembly, called a compression ring, near an uppermost portion of the piston. The compression ring is designed to seal during up-stroke of the piston to compress gases within the combustion chamber. Further, the piston ring assemblies also prevent excess lubricating oil from entering the combustion chamber during down-stroke of the piston. Typically, a second piston ring, called an oil ring, is placed below the compression ring to prevent oil from escaping into the combustion chamber.
Outer peripheries of the piston ring assemblies contact a wall of the cylinder to form the seal. As a result of manufacturing tolerances and material expansion due to heat generated by the engine, the fit of the piston ring assemblies within the grooves fluctuates. Accordingly, oil or combustion gases may still escape through a gap between the surfaces of the piston ring assembly and its associated groove. The escape of oil and combustion gases results in a less efficient engine.
Accordingly, there is a need for an improved piston ring assembly that increases engine efficiency by providing an effective seal between not only the outer periphery of the piston ring assembly and the cylinder wall, but also between surfaces of the piston ring assembly and the associated annular groove of the piston.